This invention relates to an integrated circuit Hall switch and more particularly to such an integrated circuit including two Schmitt trigger circuits responding to the output from a single Hall element therein to provide two trains of non-overlapping current pulses to two inductive loads, e.g. stator windings on a D.C. brushless motor.
In an integrated circuit described in the patent to Avery, U.S. Pat. No. 4,443,716, issued Apr. 17, 1984 and assigned to the same assignee as is the present invention, there is described an integrated circuit Hall-switch including a Hall element, a Hall-voltage amplifier followed by a Schmitt trigger circuit. For use as a magnetic field sensor, this integrated circuit has an output that changes from one level to another level when the ambient magnetic field exceeds a predetermined magnitude. This I.C. (integrated circuit) Hall-switch has operate and release points that are adjusted as desired by mounting a magnet to the IC and partially demagnetizing the magnet.
In my patent application Ser. No. 912,709 filed Sept. 29, 1986, I have described another method for adjusting the hysteresis characteristic of such an I.C. Hall switch. Briefly, this entails providing in the I.C. a string of series connected resistors across one of the differential inputs of the Schmitt circuit. All but one of these resistors are shorted by a metal film conductor. By selectively opening certain of these shorting conductors, the string resistance is adjusted to adjust in turn the operate (and release) points of the I.C. Hall switch.
Integrated circuits or I.C. Hall switches of such kinds find use as rotor position sensors in D.C. brushless motors that have magnetized rotors. The stator windings are excited by a solid state commutating circuit. Typically, such a motor has a two-magnetic-pole rotor, four stator windings. Two Hall switches may be mounted, between stator windings, 90.degree. apart. Responding to the rotor field, the output from each Hall sensor provides pulses of current to one pair of stator windings such that when one is on the other is off. This is typically accomplished by circuitry in the Hall sensor that provides a differential (two complimentary) output, each phase of which, respectively, is for exciting one of a pair of stator windings.
A fuller description of D.C. brushless motors construction including the use therein of Hall devices as rotor position sensors is provided in the book Direct Current Machines by M. Say and E. Taylor, second edition, Pitman and Son, Ltd; London 1985: pp. 79-80, 121-124 and 296-300.
It has been observed, however, that electronically-commutated brushless D.C. motors tend to generate objectionable acoustic noise.
It is an object of this invention to provide a commutation circuit that reduces such acoustic noise.
It is a further object of this invention to provide a commutation circuit including a pair of integrated Hall-switches that are capable of driving a pair of stator windings in a D.C. brushless motor by generating a pair of binary output signals that deviate from a mutually complimentary relationship only on account of having nonsimultaneous changes from one binary state to the other in response to changes in the ambient magnetic field strength.